1,N(6)-ethenoadenine (epsilonA) is a highly mutagenic lesion that is excised from human DNA by the enzyme alkyladenine DNA glycosylase (AAG). In an effort to understand the intrinsic properties of 1,N(6)-ethenoadenine, we examined its gas phase acidity and proton affinity using quantum mechanical calculations and mass spectrometric experimental methods. We measure two acidities for epsilonA: a more acidic site (DeltaH(acid) = 332 kcal mol(-1); DeltaG(acid) = 325 kcal mol(-1)) and a less acidic site (DeltaH(acid) = 367 kcal mol(-1); DeltaG(acid) = 360 kcal mol(-1)). We also find that the proton affinity of the most basic site of 1,N(6)-ethenoadenine is 232-233 kcal mol(-1) (GB = 224 kcal mol(-1)). These measurements, when compared to calculations, establish that, under our experimental conditions, we have only the canonical tautomer of 1,N(6)-ethenoadenine present. We also compare the gas phase acidic properties of epsilonA with that of the normal bases adenine and guanine and find that epsilonA is the most acidic. This supports the theory that AAG and other related enzymes may cleave damaged bases as anions. Furthermore, comparison of the gas phase and aqueous acidities indicates that the nonpolar environment of the enzyme enhances the acidity differences of epsilonA versus adenine and guanine.

Advanced large-scale electrochemical energy storage requires cost-effective battery systems with high energy densities. Aprotic sodium-oxygen (Na-O2) batteries offer advantages, being comprised of low-cost elements and possessing much lower charge overpotential and higher reversibility compared to their lithium-oxygen battery cousins. Although such differences have been explained by solution-mediated superoxide transport, the underlying nature of this mechanism is not fully understood. Water has been suggested to solubilize superoxide via formation of hydroperoxyl (HO2), but direct evidence of these HO2 radical species in cells has proven elusive. Here, we use ESR spectroscopy at 210 K to identify and quantify soluble HO2 radicals in the electrolyte-cold-trapped in situ to prolong their lifetime-in a Na-O2 cell. These investigations are coupled to parallel SEM studies that image crystalline sodium superoxide (NaO2) on the carbon cathode. The superoxide radicals were spin-trapped via reaction with 5,5-dimethyl-pyrroline N-oxide at different electrochemical stages, allowing monitoring of their production and consumption during cycling. Our results conclusively demonstrate that transport of superoxide from cathode to electrolyte leads to the nucleation and growth of NaO2, which follows classical mechanisms based on the variation of superoxide content in the electrolyte and its correlation with the crystallization of cubic NaO2. The changes in superoxide content upon charge show that charge proceeds through the reverse solution process. Furthermore, we identify the carbon-centered/oxygen-centered alkyl radicals arising from attack of these solubilized HO2 species on the diglyme solvent. This is the first direct evidence of such species, which are likely responsible for electrolyte degradation.

We apply the matrix product state (MPS) method to propagate the hierarchical equations of motion (HEOM). It is shown that the MPS approximation works well in different type of problems, including boson and fermion baths. The MPS method based on the time-dependent variational principle is also found to be applicable to HEOM with over one thousand effective modes. Combining the flexibility of the HEOM in defining the effective modes and the efficiency of the MPS method thus may provide a promising tool in simulating quantum dynamics in condensed phases.

A series of binuclear ruthenium-alkynyl complexes that are bridged by thiophene groups (thiophene, bithiophene, and terthiophene) have been synthesized. All of these complexes have been well-characterized by NMR spectroscopy, X-ray diffraction, and elemental analysis. The electronic properties of these complexes have been examined by using cyclic voltammetry, UV/Vis/NIR and IR spectroscopy, electron paramagnetic resonance (EPR) spectroscopy, and density functional theory (DFT) calculations. Electrochemical results showed that the potential difference (ΔE) and comproportionation constant (Kc) decreased with increasing size of the thiophene bridging unit. The UV/Vis/NIR spectra and TDDFT calculations of the monocations indicated that the NIR transitions displayed aromatic bridging character. EPR studies of the mono-oxidized radical species further demonstrated that the unpaired electron/hole was delocalized over both metals and the bridging ligand and established significant participation in the ligand oxidation.

We develop new methods to efficiently propagate the hierarchical equations of motion (HEOM) by using the Tucker and hierarchical Tucker (HT) tensors to represent the reduced density operator and auxiliary density operators. We first show that by employing the split operator method, the specific structure of the HEOM allows a simple propagation scheme using the Tucker tensor. When the number of effective modes in the HEOM increases and the Tucker representation becomes intractable, the split operator method is extended to the binary tree structure of the HT representation. It is found that to update the binary tree nodes related to a specific effective mode, we only need to propagate a short matrix product state constructed from these nodes. Numerical results show that by further employing the mode combination technique commonly used in the multi-configuration time-dependent Hartree approaches, the binary tree representation can be applied to study excitation energy transfer dynamics in a fairly large system including over 104 effective modes. The new methods may thus provide a promising tool in simulating quantum dynamics in condensed phases.

This work describes syntheses and electrochemical, spectroscopic, and bonding properties in a new series of dinuclear ruthenium(II) complexes bridged by polyaromatic (biphenyl, fluorene, phenanthrene, and pyrene) alkynyl ligands. Longitudinal expansion of the π-conjugated polyaromatic core of the bridging ligands caused a reduced potential difference between the anodic steps and reinforced their bridge-localized nature, as evidenced by UV/vis/near-IR and IR spectroelectrochemical data combined with DFT and TDDFT calculations. Importantly, the intricate multiple IR ν(CC) absorption bands for the singly oxidized states imply a thermal population of a range of conformers (rotamers) with distinct electronic character. This behavior was demonstrated with more accurate DFT calculations of selected nontruncated 1e − oxidized complexes in three different conformations. The combined experimental and theoretical data reveal that thermally populated rotamers featuring various mutual orientations of the ligated metal termini and the bridging diethynyl polyaromatic moieties have a significant impact on the electronic absorption and ν(CC) wavenumbers of the singly oxidized systems. ■ INTRODUCTIONSince the first report of the Creutz−Taube ion [(H 3 N) 5 Ru(μ-pyrazine)Ru(NH 3 ) 5 ] 5+ , there have been numerous experimental and theoretical attempts to elaborate the properties of related symmetrical diruthenium complexes due to the surprising stability of the Ru II Ru III mixed-valence states. 1 It has been well documented that diruthenium complexes with metal centers linked by π-conjugated bridges allow for facile electron transfer along the whole molecular framework. Accordingly, pertinent studies have concentrated on elaborately selecting the conjugated bridging ligands and tuning the electronic effect of the ancillary ligands to subtly modulate the intramolecular electron-transfer properties in mixed-valence complexes. 2,3 We have focused on dinuclear ruthenium complexes with a particular type of redox-active terminals, viz., (P,P′-dppe)(η 5 -C 5 Me 5 )Ru, which are interconnected by the conjugated bridge participating in the redox behavior. These complexes may become attractive candidates for molecular wires. 4 Furthermore, a range of studies in our laboratory as well as other literature reports have convincingly elucidated that the horizontal scaling of π-conjugated bridges results in poor solubility and chemical stability of the oxidized species and an attenuation of the electronic transport in a mixed-valence system; introducing aromatic rings such as benzene or a heterocycle in the spacer can constitute an attractive alternative to improve this instability and eventually to tune their physical or even chemical properties. 5 Therefore, a reasonable control of the length and appropriate extension of the conjugation in the bridging ligands can afford improved stability and allow for efficient tuning of the electron-transfer properties. 6 In addition, numerous studies have indicated that fluorene, phenanthrene, and pyrene ...

We study the ground state properties, potential energy curves and potential energy surfaces of the superheavy nucleus 270 Hs by using the multidimensionally-constrained relativistic mean-field model with the effective interaction PC-PK1. The binding energy, size and shape as well as single particle shell structure corresponding to the ground state of this nucleus are obtained. 270 Hs is well deformed and exhibits deformed doubly magic feature in the single neutron and proton level schemes. One-dimensional potential energy curves and two-dimensional potential energy surfaces are calculated for 270 Hs with various spatial symmetries imposed. We investigate in detail the effects of the reflection asymmetric and triaxial distortions on the fission barrier and fission path of 270 Hs. When the axial symmetry is imposed, the reflection symmetric and reflection asymmetric fission barriers both show a double-hump structure and the former is higher. However, when triaxial shapes are allowed the reflection symmetric barrier is lowered very much and then the reflection symmetric fission path becomes favorable. MDC-RMF model, superheavy nuclei, potential energy surface, fission barrier, reflection asymmetry, triaxial deformation PACS number(s): 21.10.-k, 21.60.Jz, 27.90.+b, 23.70.+j Citation: Meng X, Lu B N and Zhou S G, Ground state properties and potential energy surfaces of 270 Hs from multidimensionally-constrained relativistic mean field model, Sci.

A series of dinuclear ruthenium alkynyl and vinyl complexes bridged by carbazole, dibenzofuran, dibenzothiophene, and fluorenone have been prepared, and some representative molecular structures have been determined. The electrochemical and spectroscopic properties of the compounds were explored by cyclic voltammetry (CV), square-wave voltammetry (SWV), and in situ infrared and UV/Vis/near-IR spectroelectrochemical methods. The electrochemical results